In the present domestic and world political climate, U.S. military forces are faced with a growing number of situations in which less-than-lethal response options are essential. Recent examples include Somalia, Cuban refugee camps and Haiti, as well as riots in Los Angeles. In these types of situations, where military, political and humanitarian objectives preclude the use of lethal force except when personnel are in immediate danger, the individual soldier must have less-than-lethal options available to him or her to warn, deter, delay, or incapacitate a wide range of adversaries.
Low-energy lasers can be effective, non-lethal weapons for a variety of military missions as well as civilian law enforcement applications. Through the effect of illumination, glare, flashblinding and psychological impact, lasers can create hesitation, delay, distraction, temporary visual impairment, and reductions in combat and functional effectiveness when used against local inhabitants trying to steal supplies, intruders, military and paramilitary forces, terrorists, snipers, criminals and other adversaries. Furthermore, if continuous-wave or repetitively pulsed lasers having the required intensity are used, these effects can be created at eye-safe exposure levels below the maximum allowed by international safety standards. The low-energy laser systems used to produce these effects are called laser visual countermeasure devices.
As disclosed in the present invention, additional specific applications for which such lasers would enhance effectiveness include security for military and industrial facilities, apprehension of unarmed but violent subjects, protection from suspected snipers, protection from assailants and crowd/mob control. Another important class of applications are those which limit the use of potentially lethal weapons because innocent people are present. These include hostage situations, protection of political figures in crowds, airport security, and prison situations where guards are present. A similar situation occurs when use of firearms or explosives in the battlefield may cause unacceptable collateral damage to friendly personnel, equipment or facilities (including aircraft or electronic equipment). Finally, there are portable applications, such as raids on hostile facilities and hostage rescues, where even a few seconds of distraction and visual impairment can be vital to the success of the mission.
Until recently, the relatively large size of laser-producing components have prevented the use of laser technology in personal protection or security applications.
In recent years, however, compact laser-producing components have made the benefits of laser technology available to numerous applications, such as compact disc players, medical tools and welding appliances.
Lasers are capable of a wide range of effects on human vision which depend primarily on the laser wavelength (measured in nanometers), beam intensity at the eye (measured in watts/square centimeter), and whether the laser is pulsed or continuous-wave. These effects can be divided into three categories: (1) glare; (2) flashblinding; and (3) retinal lesion.
The glare effect is a reduced visibility condition due to a bright source of light in a person's field of view. It is a temporary effect that disappears as soon as the light source is extinguished, turned off or directed away from the subject. If the light source is a laser, it must emit laser light in the visible portion of the wavelength spectrum and must be continuous or rapidly pulsed to maintain the reduced visibility glare effect. The degree of visual impairment due to glare depends on the ambient lighting conditions and the location of the light source relative to where the person is looking. In bright ambient lighting, the eye pupil is constricted, allowing less laser light into the eye to impair vision. Also, if the laser is not near the center of the visual field, it does not interfere as much with an individual's vision.
In contrast, the flashblind effect is a temporary reduction in visual performance resulting from exposure to any intense light, such as those emitting from a photographic flashbulb or a laser. The nature of this impairment makes it difficult for a person to discern objects, especially small, low-contrast objects or objects at a distance. The duration of the visual impairment can range from a few seconds to several minutes, and depends upon the amount of light intensity employed, the ambient lighting conditions and the person's visual objectives. The major difference between the flashblind effect and the glare effect is that visual impairment caused by flashblind remains for a short time after the light source is extinguished, whereas visual impairment due to the glare effect does not.
The effectiveness of a given laser as a security device is directly related to how bright the laser appears to the eye. The apparent brightness of a laser is a function of the laser intensity at the eye and the laser wavelength. The intensity at the eye, measured in watts per square centimeter, can be increased by control of the laser output power level and laser beam size. The wavelength, however, is a function of the type of laser employed and is therefore more severely constrained by the limited laser options available which are suitable for the security device applications of the present invention.
If the intensity of a laser beam at the eye exceeds a certain level, injury to the retina may occur in the form of lesions (i.e., small burns at the focal spot of the laser beam). To ensure that laser security devices are non-damaging to the human eye, the intensity present at the subject's eye must be below the threshold for permanent damage. The definitive laser safety parameter as defined by the American National Standards Institute in ANSI Z136.1-1993 is the Maximum Permissible Exposure (MPE) which is measured in watts per square centimeter for continuous (non-pulsed) laser beams. If the laser intensity anywhere within the beam diameter exceeds the MPE, the possibility of retinal injury exists. The value of the MPE for short (e.g., quarter second) exposures to visible laser light is 2.55 milliwatts per square centimeter.
Prior art in the area of self-contained laser devices focus on low-power lasers (i.e., output laser power of less than 5 milliwatts) such as those used in laser pointers (e.g., Edmund Scientific Stock Number P38,914), surveying equipment, alignment lasers, and laser gun sights. For these devices, the issues that are important for eye-safe laser security devices (i.e., maximum beam intensity, beam intensity profile, and beam uniformity) do not play a significant role in design. Furthermore, with these very low-power lasers, diode cooling and thermal management are not important issues. As such, the present invention resolves six key problems which must be considered in the design of laser illuminator subsystems for eye-safe laser security devices: (1) distribution of laser power within the beam diameter, (2) control of the laser power output, (3) size, (4) mechanical stability, (5) thermal management, and (6) impact of the laser on the adversary.
The first problem examines the laser power. The laser power within a typical laser beam is not evenly distributed throughout the diameter of the beam. This means that the laser power usually concentrates in one or more intensity peaks within the beam. The output beam from a semiconductor laser diode (i.e., laser) is particularly poor in this respect, having a sharply peaked intensity distribution. Laser diode beams also provide design difficulties because they are highly elliptical and exhibit sufficient astigmatism to redistribute the beam intensity as the distance from the laser increases. FIG. 1 shows the intensity profile of such a beam. For eye safety purposes, it is desirable to minimize the number and magnitude of these "hot spots." Also, because the eye perceives apparent brightness based on the average intensity within the beam rather than the peak intensity, the effectiveness of a laser security device is enhanced if the power is distributed as evenly as possible throughout the beam. Preferably, the optimum laser intensity distribution is a smooth curve with minimal peaking at the center of the beam and little astigmatism, such as shown in FIG. 2. As such, the maximum value of the laser intensity is just below the MPE value given above.
The second design problem, also related to effectiveness of the laser and eye safety, is control of the maximum power output of the laser over time. If the laser output power increases, the maximum intensity will exceed the MPE. Conversely, if the laser output power decreases, the laser's effectiveness will be reduced. Most eye-safe laser security devices discussed in the parent invention employ semiconductor diode lasers operating in the red wavelength portion of the light spectrum. The output power of such semiconductor diode lasers varies significantly with drive-current fluctuations, temperature, and cumulative use. It is therefore important to employ a means for controlling the output power to maximize safety and effectiveness.
The third problem in laser illuminator design for laser security devices is the size of the unit. Until recently, the relatively large size of laser-producing components have prevented the use of laser technology in personal protection or security applications. However, the development of semiconductor laser diodes operating at appropriate wavelengths and power outputs, and the availability of surface-mounted electronic integrated circuits for power control, have made hand-held laser security devices possible. The more compact these components are, the more useful they are to military and police personnel already overloaded with equipment.
The fourth problem relates to the mechanical stability of both the laser and the optical system. The position of the laser source relative to the collimating lens must be accurately maintained. The mechanical means for mounting these two components relative to each other must account for fine adjustment during assembly (for approximately accurate distancing and alignment between the laser source and the lens), and subsequently, maintain that alignment during rough use.
The fifth problem is control of the heat generated by the laser diode, the cooling subsystem and the electronic circuits. These three sources combine to produce several watts of waste heat which must be conducted away from the temperature-sensitive semiconductor laser diode. In larger laser systems, a fan could be employed for that purpose. However, in compact, hand-held laser security devices, heat sinks should be employed to provide the necessary thermal management. Moreover, the compact nature of the hand-held laser security devices must be taken into account, since the temperature rise is inversely related to heat sink volume.
The final problem is the desire to maximize the psychological and physiological impact that the laser security device imparts to the adversary. Field tests have demonstrated that a round, uniform, red laser beam (e.g., one to two feet in diameter) which is directed towards or shined upon an adversary's chest provides a strong psychological impact. If the engagement is escalated by moving the beam to the subject's eyes, the physiological response of the eye to such bright light hinders further action. Moreover, it is deemed desirable to have the laser beam quickly or repetitively flash on and off. Studies have shown that a frequency of 7 to 9 Hertz is optimal for inducing disorientation in a person.
The present invention resolves these design issues by providing a laser illuminator that integrates the optical, laser, power control, and thermal management means into a single, small, compact (or, modularized) unit. The present invention also employs a novel fiber optic means for producing a smooth, relatively flat beam intensity distribution to optimize effectiveness and eye-safety. The present invention is suitable for use in any embodiment of the eye-safe laser security devices described in the referenced patent and will enhance their effectiveness, safety, and usefulness. The present invention also provides a sealed module that is easily replaced when it fails, or upgraded to an improved design based on new technological advances.
Accordingly, it is an object of the present invention to provide a single, compact, high-powered laser illuminator module to succeed the separate optical, laser, power control, and thermal management subsystems in prior art laser security and/or illumination devices.
It is a further object of the present invention to provide a self-contained laser illuminator module having a fiber-optic means for converting the sharply peaked, highly elliptical, astigmatic output beam from a semiconductor laser diode into a relatively smooth, uniform, circular laser beam suitable for effective use in an eye-safe laser security device.
It is also an object of this invention to provide a laser illuminator module having a means to flash the laser beam on and off at a nominal rate of 8 Hertz to provide disorientation and added psychological impact to the adversary.
It is also an object of this invention to provide a laser illuminatormodule having a mechanical means for adjusting the alignment of optical components to achieve optimum output of the laser illuminator which also serves to maintain that alignment during use.
It is also an object of the present invention to provide a smaller, light-weight, portable laser illuminator module through compact integration of electronic control means required for operation.
It is also an object of the present invention to provide a laser illuminator module having a means to protect the semiconductor laser diode from damage due to overheating through a novel heat sink design and an integral, self-resetting thermal fuse.